Project Summary: The internal mechanics of proteins ? the coordinated motion of amino acids and the pattern of forces constraining these motions ? connects protein structure and function. The biologically relevant motions are potentially quite subtle, distributed widely over the tertiary structure, and likely to cover a broad range of time scales. Current biophysical methods do not offer a route to a complete description of these motions, a problem that severely limits our understanding of protein structure, function, and evolution. Here, we propose a completely new approach to this problem involving the application of strong electric fields to protein crystals with simultaneous time-resolved x-ray diffraction to observe the resulting motions in spatial and temporal detail. Preliminary work provides strong justification for development and application of this method, called EF/TRX, and motivates a set of interesting experiments to explore the power of this approach for exposing the structural basis for complex protein functions. EF/TRX involves considerable technical and conceptual innovations, but the completion of the work described here should enable broad usage of this new method by the scientific community and stimulate further development. More fundamentally, the experiments proposed will lay the foundation for understanding the mechanical basis of protein function.